In the related art, a large vehicle such as a truck or a bus employs pneumatic brake device using compressed air as an operating fluid which operates a brake chamber. In the type of brake device, a vehicle compressed air supply device supplying compressed air to each brake chamber is mounted.
The vehicle compressed air supply device includes an air compressor and retains the compressed air discharged from the air compressor in an air tank, and supplies the compressed air inside the air tank to each brake circuit if required. In addition, the vehicle compressed air supply device includes pressure protection valves corresponding to each of brake circuits respectively. When one of the brake circuits is failed, the pressure protection valve corresponding to the brake circuit, which is failed, is closed and thereby the pressure protection valve has a function to protect the other brake circuits which are not failed.
In addition, recently, from the viewpoint of further safety, when a pressure of the compressed air supplied to a service brake circuit does not reaches a predetermined pressure value, the pressure protection valve corresponding to a parking brake circuit is closed and thereby the pressure supply to the parking brake is stopped. Usually, the service brake actuates a braking force with the pressure of the supplied compressed air. Meanwhile, the parking brake is a spring brake using a bias force of a spring and is configured such that a braking force is released by the pressure of the supplied, compressed air. Thus, a control valve is provided upstream the pressure protection valve corresponding to the parking brake circuit and in a case where the service brake is not actuated because the pressure of the compressed air supplied to the service brake circuit is not enough, the control valve is closed and thereby the pressure supply to the parking brake circuit is stopped and the parking brake cannot be released (for example, PTL 1).